Multiple furnace control



Filed April 18, 1945 a m f f a m a o W p m mm m M HC a n H 0 RR R do a 3 fl E H E5 5 N 4 2 ma 1 R w a w Fl 1 m H fl w w 5 9 fl .L I l 1 ATTORNEY Patented Get. 19, 1948 MULTIPLE FURNACE CONTROL Harold A. Strickland, Jr., Grosse Pointe Park, Mich, assignor, by mesne assignments, to The Ohio Crankshaft corporation of Ohio Compa Cleveland, Ohio, a

Application April 18, 1945, Serial N0. 589,054

7 Claims. I

This invention relates to control apparatus for power units with particular application to induction heating furnaces.

In the operation of several power units such as induction furnaces from the same power source, it is: desirable frequently that the power be applied to each unit separately so that too great a load may not be placed on the power source. If connection to the source is made manually from unit to unit'the time loss over the period of operation of the equipment may be considerable, resulting iina substantial reduction in output. Also, in op- ;erating a bank of power units such as induction furnaces, not only is it desirable that the shift- :ingpf power from furnace to furnace be immediate andautomatic, but it is also important that .means be provided to prevent operation of any one unit while the other is in operation.

Among the objects of the invention, therefore, ijS'ItO; provide a control apparatus which will insure automatic and immediate power connection :atothe individual power units consecutively.

Another important object is to provide control .means which will prevent operation of any one of the units ifat the same time another of the uni-tS is in operation.

object also is to provide apparatus as above "indicated which will not prevent individual use .o'fany. one unit to the exclusion of the other units.

Other objects of the invention will become ap- 'parent on consideration of the following description. and the related drawingpertaining to a preferredmodification of the invention in which Fig ure 1 is a circuit diagram of the apparatus; and Figure '2 is a detail illustrating operation of the load switches.

Referring to the drawing, Figure 1 is a wiring diagram of the control circuit applicable to a D ra'lity of power units such as induction furnaces.

In my co-pending application Serial No. 384,503 filed Mar-ch21, 1941, now Patent No. 2,408,350, is-

sued September 24, 1946, I have described the structural features and electrical circuit of an induction furnace suitable for miscellaneous bar heating. This furnace equipment is adequate for single unit operation but under conditions of multiple unit, operations where the power is derived from a single source or where the heating coils are assembledin a single casing with connections to a common bus bar system, there is lack of provision for. operation of eachof the separate heating units consecutively and with immediate and automatic. transfer of power from one unitto the Connected across the mains tifier and transformerunit 8 for supplying a rectified current to the highv frequency generator field 2 other after heating operationis respectively completed in the heating coils.

The circuit of Figure 1 illustrates one mode which may be preferred of securing this desirable transfer from one unit to the other.

The numeral i indicates the source of power for the heating equipment illustrated and is desirably alternating current at commercial frequency. From this source through the manual switch 2 and transformer 3 current is supplied to the main control switch of furnace coilsA and B through a series of relaycoils and switches which are in general parallel in both of the furnace circuits. As will become apparerrtthe relaysan plicable to the A furnace are indicated by the letter A with subscript numerals with relay contact switches corresponding and the relays and contact switches of the B furnaceby the letter'B with appropriate sub-script numerals.

From the transformer secondary 4 of the transformer 3 a current is passed to the main conductors 5 and 6 for supplying power to the various relays and other equipment. An indicatinglamp 1 is connected across the secondary 4 to indicate application of power to the main circuits 5 and 6,

also is the field recof the heating circuit. The fieldtransformercon- ,tactor relay coil 9 is connected in series with a manual switch 10 and with the door or other structure switch ll, coolant pressure switch l2 and over-load contact switch 13 between the mains 5 and .6. At the point l4 between manual switch l0 and door switch I I a conductor l5 leads to the intermediate .contactor relay coils Al and BI Connected also between the conductors Sand 15 are the relays A2, A3, and A4 and the corresponding relays B2, B3, and B4. The A2B2 relays constitute the clutch coils for the timer i6 and H respectively.

The coils A3 and B3 form the anti-reset coils for the A and B sections. Coils A4 and B4 form the contactor pilot relays for sections A and B. Coils A5 and B5 connectedacross conductors 5 and 6 constitute the main contactor relays for energizing of the relay switches inthe heating circuits of furnaces A and B.

Following the individual branch circuit of the relays more specifically, Al connects between conductors 5 and l5-through the normally open contact switch A212, normally open contact switch A3b, load switch Li. and normally closed manual stop switch 8. The load switch Ll is opera-tively related to the heating coil of the A furnace so that when the load is placed in the coil theswitch normally open relay switch open relay switch Bla.

connections to will be closed. Figure 2 illustrates .diagrammatically the action of the load switches LI and L2 by a push-out rod in engagement with the workpiece. When the workpiece is completely inside the heating coil 24, Ll switch closes and L2 switch opens. Switches L3 and L4 are similarly operated.

The branch circuit including the clutch coil A2 includes the normally open relay contact AM, this contact switch being shunted by the normally closed relay switch Blb in series with the normal- 1y open contact switch A4b, further connection being made to the conductor l5 through the conductor l9 to the point 26 between switches A2b, A3b in the Al circuit.

The A3 branch circuit includes the normally closed load switch L2 bypassed by the normally open contact switch A3a from which connection is made to the point 21 between load switch Ll and stop switch [8 in the Al circuit. L2 switch is open when a load is in the A furnace.

The A4 branch circuit in addition to the relay A4 includes the normally closed relay contact switch Al 0, and the normally open starting switch 22 with the normally open relay switch A la in parallel therewith, the circuit continuing to conductor l9 and the point 20 in the Al branch circuit.

The A5 branch circuit includes the normally open, switch Ala from which connection is made directly to the main conductor 6. The relay A5 is bypassed by the indicating lamp 23. Also'the end of coil Al between the coil and contact switch A21) is connected to the end of coil A2 at conductor 5 through a timer mechanism indicated by the term Timer. The heating circuit of furnace A is indicated by the heating coil 24 there being the main contact switch A5a in series therewith. with appropriate connections to the high frequency terminals 25. The relay load and manual switches in the B furnace circuit are identical as to number and nature of switches. The Bl coil branch includes normally open relay switches 13% and B3b as well as, load switch L3 normally open and the normally closed manual stop switch 30.

" The B2 branch circuit includes the normally open relay switch B2a and theshunted circuit including normally closed relay switch Alb and B la.

Q The B3 branch circuit includes the normally closed load switch L6 and the shunted normally open relay switch 33a.

The branch circuit B4 includes the normally closed relay switch Blc, and normally open starting switch 26 and normally open relay switch B lb connected in parallel, the circuit continuing to point 2'! in the Bl circuit.

' The B5 branch circuit includes the normally The B furnace circuit heating coil 28 this-coil having the power terminals 29 through the normally open contactor switch 135a.

'In describing the operation of the circuit it comprises the "should be kept in mind that relay switches are identified with the operating relay coil by the first two indicia. For example, relay switch Alb is operated by relayAl and is one of several contactswitches operated by this relay designated Ala, Alb and Ale. Similarly, relay Ab is operated by relay A4 and is one of two relay switches operated by this coil.

In operation, the coolant is supplied'to'the various conductors and tubing of which the unit is constructed bringing about closure of the pressure switch l2. .The switch in the coil 9 circuit ,the normally closed load switches L2 and L l. Energization of coils A3 and B3 brings aboutclosure of the lock and relay switches A3a and 33a and Al and BI circuit switches A312 and B31). Assuming that there is no load in the B furnace, a load is now placed in A furnace bringing about closure of the Ll load switch in the Al circuit and opening of L2 load switch in the A3 circuit. Since A3a is locked in by the active coil A3 the opening of the L2 switch does not disturb the closure of the Alib switch in the Al circuit. Manual starting switch 22 is now closed causing A l relay coil to become energized, A ia switch closing and locking in the circuit around the starting switch. Also open switch A ib in the A2 circuit is closed bringing about energization of the timer clutch coil A2 which locks itself in through closure of switch A'Za. Switch A2b in the Al circuit is also closed by coil A2 thus energizing the coil Al and the timer l6 and bringing about the initiation of the timing cycle. Al closes switch Ala in the A5 circuit, energizing coil A5 which in turn closes the main contactor switch AM in the load circuit of coil 24. Al also opens the normally closed switch Alc in the Ad circuit to prevent closure of a circuit through the starting switch 22 and consequently switch Ada opens. Switch Alb in the B2 branch of the B furnace also opens thus preventing any possibility of a circuit being established through the timer coil B2 to initiate a heating or power cycle in the B furnace.

The various switch actions mentioned. above take place after the closure of the A starting switch 22 and with the energization of the timer coil Al a static condition exists while the timer carries through its timing period. At the end of the timer period the timer mechanism acts to release contact switch A2b thus de-energizing coil Al and releasing switches Ala in the main. circuit A5, Alb in the B2 circuit of the B furnace and Ale inthe A4 circuit. Opening of Ala opens the main contactor switch Ata in the power circuit of the A furnace; release of switch Alb closes the. same making possible energization of the B furnace; and release of Alc closes the switch to permit completion of a starting circuit when desired. The completion of the timing cycle however does not release switch A2a which remains closed and consequently the timer is not reset by the termination of the timer period. To reset the timer it is necessary that clutch coil A2 be de-energized and this can be accomplished only by removal of the load from the heating coil of the A furnace to open the L! switch or through the actuation .of the manual stop switch l8 or the over-load switch l3, the pressure switch l2, the dooror miscellaneous switches indicated by the numeral close this circuit through the clutch coil B2 of the timer. However the B furnace may be loaded and the starter switch 26 in the B4 circuit closed to condition the B circuit for immediate actuation on closure of switch Alb in the B2 circuit. The procedure is to place the load in the B furnace immediately after the normal heating cycle has begun in the A furnace. This closes load switch L3 in the BI circuit and as soon as switch B3b adjoining the load switch is closed voltage is placed on the B4a switch pendin closure of the is placed on the starting switch 26 so that when this switch is closed coil B4 is energized closing 3% switch and 34a in the B2 circuit. The B circuit is now in condition to start the heating cycle in the B furnace as soon as switch Alb, which is held open by the Al coil, is closed and this tion of the heating cycle in the A circuit. Immediately thereafter B2 is energized closing BZa and B22; switches, energizing Bl coil, closing Bla switch in the main contactor circuit B5, and thus closing the power switch B5a in the B furloaded and the manual starting switch 22 closed so as to condition the A circuit for immediate energization for a new heating cycle as soon as the load is removed from the B furnace. This alternate loading and heating is continued as desired.

It thus appears from the above description that two furnaces A and B supplied from the same power source may be kept continuously in sequential operation automatically and without any appreciable time interval between the completion of the heating cycle in the one furnace and the energization of the heating cycle in the other furnace. It also appears from this description that if the operator fails to remove the load from one furnace another furnace can be operated after the completion of the heating cycle in the loaded furnace. Also it is evident that the circuit does not prevent continued operation of one only of the furnaces provided there is no load in the other furnace. In the event that the pressure in the cooling circuit drops to a point causing opening of switch i2 or over-load switch l3 opens, the entire circuit will be de-energized but on resumption of current through the switches a new heating cycle will not develop in the furnace in which the cycle was interrupted unless the load is first removed from the furnace. This isdefinite notice to the operator that the load has been partially heated only and will not stand a new complete cycle of heat. In this connection use may be made of manual swiches l8 and 39 to break the heating circuit at the proper time for securing full heat treatment of the prior partially heated load.

The showing made is diagrammatic and it is apparent that modification may be made to suit special conditions met with in practice. The invention therefore is not intended to be limited except by the scope of the following claims.

What is claimed is:

1. In power equipment, a first power unit, a second power unit, means for supplying power to said units, control means for initiatin a power cycle in the first unit, and means controlled by the first unit control means for conditioning said second unit for initiation of a power cycle therein only after cessation of power flow in the first unit.

2. In power equipment, a first power unit adapted to receive a load, a second power unit adapted to receive a load, means for initiation and completion of a power cycle in each of said units, and means for preventing initiation of a power cycle in both of said units succeeding an interrupted power cycle in one of said units without removal of the load from both of said units.

3. In power equipment, a first induction heating coil adapted to receive a load, a second induction heating coil adapted to receive a load, a common source of power for said coils, timer means for timing a heating cycle separately in each coil, load control means for preventing a heat cycle in either coil without a load in the coil, and control means for preventing a heat cycle in either coil while a heat cycle is progressing in the other coil.

4. In power equipment, a first induction heating coil adapted to receive a load, a second induction heating coil adapted to receive a load, a common source of power for said coils, timer means for timing a heating cycle separately in each coil, load control means for preventing a heat cycle in a coil without a load in that coil, control means for preventin a heat cycle in either coil while a heat cycle is progressing in the other coil, and means for preventing a renewed cycle in either one of said coils after an interrupted cycle in that coil, without first removing and replacing the load in that coil.

5. In power equipment, a first power unit, a second power unit, means for supplying power to said units from a common source, control means for initiating a power cycle in the first unit, control means for initiating a power cycle in the second unit, and means actuated by the first unit control means for conditioning said second unit for initiation of a power cycle therein only after cessation of power fiow in the first unit.

6. In power equipment, a first power unit adapted to receive a load, a second power unit adapted to receive a load, means for initiation and completion or a power cycle in each of said units, means for preventing initiation of a power cycle in either of said units succeeding a power cycle in that unit, without removal of the load from that unit, and additional means for preventing initiation of a power cycle in either unit while the other unit is passing through a power cycle.

7. In power equipment, a first power unit adapted to receive a load, a second power unit adapted to receive a load, means for initiation and completion of a power cycle alternately in each of said units, and means for preventing initiation of power cycles in alternate sequence in said units succeeding a power cycle in one of said units with* out removal of the load from both of said units.

HAROLD A. STRICKLAND, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,541,600 Steenstrup June 9, 1925 2,039,851 Silverman May 5, 1936 2,066,929 Dawson Jan. 5, 1937 2,115,827 Powell May 3, 1938 2,349,813 Denneen et al May 30, 1944 2,379,463 Strickland July 3, 1945 2,402,852 Strickland June 25, 1946 

